(a) Field of the Invention
The present invention relates to communication networks in general and more particularly to protocols for inserting data onto the networks.
(b) Prior Art
The use of serial or ring communication networks for transferring data is well known in the prior art. Such networks consist of a set of stations serially connected to a communication medium. Information is transferred sequentially, bit by bit, from one station to the next. The inactive stations are bypassed while the active stations regenerate and repeat each bit. Furthermore, the stations are used as the means for attaching one or more devices (terminals, work station, computers, display, etc.) for communicating with other devices on the network.
An originating station transfers its information (message) onto the ring. The message circulates, passes one or more intermediate stations, until it arrives at the destination station where it is copied. The message remains on the ring until it arrives at the originating station where it is stripped from the ring. In some configurations, part of the stripping of messages is done by a monitor station. In addition, the monitor station may perform other types of housekeeping functions for the ring.
An access method protocol is a necessary element for the above-described ring network. The protocols are the mechanisms which enable a station to transmit on the ring. Stated another way, an access protocol gives a station the right to place its messages for transmission on the ring.
The prior art uses several different types of access method protocols. The so-called "register" insert access protocol and "token" insert access protocols are representative of the prior art. With the register insert access protocol a station seizes the opportunity to transmit whenever there is an "idle" signal on the ring. With the token insert access protocol a station has an opportunity to transmit whenever it receives a free token. The free token is usually generated by an upstream station
Although the prior art access method protocols work well for the intended purpose, they are plagued by certain defects which tend to reduce the overall efficiency of the ring networks. The register insert protocols require the introduction of relatively long delays in the ring in order that messages can be successfully stripped from the ring. The delay lengthens the time that is needed to process a message. Likewise, the "token" access protocol allows only one message to be on the ring at any particular instant of time. When the messages are relatively short, compared to the latency of the ring, only a fraction of the available bandwidth is used. Failure to use all of the available bandwidth reduces the efficiency of the ring because a series of idle patterns must be transmitted to fill up the vacancy on the ring.